What dead stars leave behind

Science · Astronomy & Astrophysics · ages 21-22

Name ______________________ Date ____________

A strongly degenerate electron gas cools while its density and composition stay fixed. How does its degeneracy pressure change?
- It stays nearly unchanged
- It falls in proportion to temperature
- It disappears without continued fusion
What provides the main pressure support inside an ordinary, non-fusing white dwarf?
- Energy from ongoing core fusion
- Electron degeneracy pressure
- Heat arriving from the surface
What is the approximate Chandrasekhar limit for a cold, nonrotating carbon-oxygen white dwarf? Give the number in solar masses, to one decimal place.
Answer: ______________
A model permits cold, nonrotating neutron stars up to 2.3 solar masses. A cold, nonrotating neutron-rich remnant has mass 2.0 solar masses. What does this comparison show?
- A stable white dwarf is required by this limit
- A black hole is required by this limit
- A stable neutron star is allowed
A Sun-like star sheds its envelope. Its remaining 0.6-solar-mass carbon-oxygen core no longer fuses and is supported mainly by degenerate electrons. Which remnant is described?
- A neutron star with nuclear-matter support
- A black hole bounded by an event horizon
- A white dwarf with electron support
How does a successful core-collapse supernova spread elements made in the star and explosion?
- It traps every heavy element inside the remnant
- It ejects element-rich layers into space
- It changes all heavy nuclei back into hydrogen
An iron-rich core can no longer gain net energy through fusion. Does this fact alone mean that all pressure support immediately vanishes?
- No; degenerate electrons can still provide support
- Yes; the presence of iron removes every source of pressure
- Yes; electrons stop exerting pressure when fusion no longer releases energy
A model caps cold, nonrotating neutron stars at 2.5 solar masses. Assume a collapsing compact remnant is cold, nonrotating and retains 5 solar masses with no further mass loss. A student predicts a stable neutron star. Which comparison challenges that prediction?
- Any mass can form a stable neutron star after collapse
- The retained mass exceeds the model's support limit
- The original birth mass alone determines neutron-star support

Answer key

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It stays nearly unchanged · In strongly degenerate matter, density mainly sets the occupied momenta and pressure. At fixed density and composition, cooling changes this pressure only slightly.
Electron degeneracy pressure · Compression fills higher-momentum electron states because electrons cannot share an identical quantum state. Their pressure resists gravity without ongoing fusion.
1.4 · Under these white-dwarf assumptions, the standard approximate mass ceiling is 1.4 solar masses. It is a support limit, not a unique prediction for every heavier core.
A stable neutron star is allowed · The remnant's 2.0 solar masses are below the stated 2.3-solar-mass maximum. The model permits a stable neutron star; the comparison alone does not identify the actual remnant.
A white dwarf with electron support · The formation history, carbon-oxygen composition and electron support identify a white dwarf. Its mass is also below the approximate 1.4-solar-mass ceiling.
It ejects element-rich layers into space · The explosion drives element-rich outer layers into surrounding space. Their material mixes with gas between stars; not every atom must be expelled from the remnant.
No; degenerate electrons can still provide support · Ending energy-releasing fusion does not erase degeneracy pressure. An iron-rich core can retain electron support until its evolving mass and physical conditions make it unstable.
The retained mass exceeds the model's support limit · Five solar masses exceed the stated 2.5-solar-mass maximum. The model excludes a stable neutron star under these assumptions; continuing collapse can form a black hole.